Contact force testing apparatus, use of such a contact force testing apparatus and method for producing such a contact force testing apparatus

ABSTRACT

A contact force testing apparatus includes a measuring sensor that can be contacted with an electrical contact element and measures a contact force (F) of a contact with the electrical contact element of an electrical connector having a male component and a female component. The measuring sensor receives the contact force in a contact region with a piezoelectric pick-up. The measuring sensor includes a plurality of piezoelectric pick-ups that are spaced apart from one another by pick-up gaps. The measuring sensor has a protective sleeve that covers the piezoelectric pick-ups and the pick-up gaps in the contact region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application Serial No.PCT/EP2016/059088, filed Apr. 22, 2016, which claims priority to SwissApplication No. 00595/15, filed Apr. 30, 2015. International ApplicationSerial No. PCT/EP2016/059088 is hereby incorporated herein in itsentirety for all purposes by this reference.

FIELD OF THE INVENTION

The invention relates to a contact force testing apparatus comprising ameasuring sensor, a use of such a contact force testing apparatus and amethod for producing such a contact force testing apparatus.

BACKGROUND

Piezoelectric material is used in many locations to pick up pressure,force and acceleration. As described in the book “Piezoelectric Sensors”by G. Gautschi, published by Springer Verlag, a piezoelectric crystalsuch as quartz (SiO₂ single crystal), calcium gallo-germanate(Ca₃Ga₂Ge₄O₁₄ or CGG), langasite (La₃Ga₅SiO₁₄ or LGS), tourmaline,gallium orthophosphate, etc. can be cut into plate-shaped or rod-shapedelements, which elements are exposed to mechanical stresses. Apiezoelectric pick-up therefore forms a capacitor in which thepiezoelectric material is disposed between two acceptor electrodes. Inthe direct piezoelectric effect, electric polarization charges arethereby produced which are proportional to the magnitude of themechanical stresses. If the electric polarization charges are producedon piezoelectric material surfaces, whose surface normal is parallel tothe acting mechanical normal stress, a longitudinal piezoelectric effectexists. If the electric polarization charges are produced onpiezoelectric material surfaces whose surface normal is perpendicular tothe acting mechanical normal stress, a transverse piezoelectric effectexists. The electric polarization charges are received as an outputsignal via acceptor electrodes. The electrical insulation resistancebetween the acceptor electrodes is 10 TΩ.

In addition to piezoelectric crystals, piezo-ceramics such as bariumtitanate (BaTiO₃), mixtures (PZT) of lead titanate (PbTiO₃) and leadzirconate (PbZrO₃), etc. and piezoelectric polymers such aspolyvinylidene fluoride (PVDF), polyvinylfluoride (PVF),polyvinylchloride (PVC), etc. can also be used as piezoelectricmaterial, as disclosed in DE2831938A1.

Electrical plug connections comprise male contact elements such ascontact plugs, contact pins etc. and female contact elements such ascontact couplings, contact sockets, etc. The male and female contactelements can be reversibly contacted with one another, for example, bymeans of a force fit. Thus, lamella contacts are known comprising acontact socket which has a plurality of lamellae spaced apart by slotsin the longitudinal direction, which lamellae hold an inserted contactpin in the area of a contact overlap on the outer side by means ofcontact force. Such contacts must frequently fulfil a standardizedcontact force. During the production of electrical plug connections itis therefore checked as part of the quality control whether the contactforce satisfies predefined desired values. At the same time, it is alsochecked whether the electrical plug connections reliably contact oneanother at elevated operating temperatures of 140° C. or even 160° C.

Piezoelectric polymers can be produced as thin layers of less than 100μm thickness, which is not possible with piezoelectric crystals. Theminimum thickness of piezoelectric crystals is 100 μm. Thus,piezoelectric polymers are predestined for very flat pick-ups. Also PVDFhas a piezoelectric sensitivity around 10 times higher than SiO₂ singlecrystal. On the other hand, the elastic modulus of PVDF is around 40times smaller than that of SiO₂ single crystal, which results in acomparatively low stiffness, with the result that PVDF can only besubjected to restricted mechanical loading, which in turn results incomparatively poor-quality output signals with high hysteresis anddeviations from linearity. PVDF also has a high temperature dependenceof the piezoelectric properties, with the result that its area of usageis restricted to temperatures less than 80° C. whereas piezoelectriccrystals such as LGS can even be used at temperatures of 600° C.

Known from DE4003552A1 is a contact force testing apparatus comprising ameasuring sensor for measuring the contact force in electrical plugconnections. The measuring sensor comprises a piezoelectric pick-upwhich consists of a layer of piezoelectric polymer which is disposed inthe direction of its longitudinal extension centrally between two layerswith acceptor electrodes. The piezoelectric pick-up is electricallyinsulated. For this purpose, a layer of electrical insulation materialis disposed above and below each layer of acceptor electrodes andrespectively one cover plate is disposed in turn thereabove andtherebelow. The contact socket to be tested can be contacted by themeasuring sensor via the cover plates, for which purpose the measuringsensor is inserted into the contact socket. The length with which themeasuring sensor is inserted into the contact socket is called contactoverlap. Width and thickness of the measuring sensor are 0.7 mm, thelength of the contact overlap is 1.0 mm.

Now, the dimensions of electrical plug connections are becomingincreasingly smaller and accordingly the contact force testing apparatusmust also be constructed increasingly smaller. A first object of thepresent invention is to further miniaturize the known contact forcetesting apparatus and to provide a method for producing such a contactforce testing apparatus. In addition, a use of a contact force testingapparatus for testing the electrical plug connections at elevatedoperating temperatures is required. Finally, the contact force testingapparatus should have the simplest possible structure, be favourable toproduce, robust and stiff, and should ensure a long lifetime, a highavailability and a high measurement accuracy. The invention also hasthese further objects.

BRIEF SUMMARY OF THE INVENTION

At least one of these objects is solved by the features described below.

The invention relates to a contact force testing apparatus comprising ameasuring sensor which can be contacted with an electrical contactelement and measures a contact force of a contact with the electricalcontact element and wherein the measuring sensor receives the contactforce in a contact region with a piezoelectric pick-up. The measuringsensor comprises a plurality of piezoelectric pick-ups. Thepiezoelectric pick-ups are spaced apart from one another by pick-upgaps. The measuring sensor has a protective sleeve, the protectivesleeve covers the piezoelectric pick-ups and the pick-up gaps in thecontact region.

An advantage of the invention compared with the prior art according toDE4003552A1 therefore lies in the fact that the measuring sensorcomprises a plurality of piezoelectric pick-ups which receive thecontact force of the electrical contact element in the contact regionmultiple times. To this end, the piezoelectric pick-ups are spaced apartfrom one another by pick-up gaps. A protective sleeve covers thepiezoelectric pick-ups and the pick-up gaps in the contact region. Theprotective sleeve thus prevents the penetration of impurities into themeasuring sensor due to its mechanical extension and as a result of itsmechanical extension is an electrical shield of the measuring sensor.The contact force testing device is therefore robust and has a highavailability and a high measurement accuracy.

The invention also relates to a use of such a contact force testingapparatus and a method for producing such a contact force testingapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail hereinafter with reference to thedrawings. In the figures

FIG. 1 shows a schematic view of an electrical plug connection which isreversibly contacted in a contact region with a contact force;

FIG. 2 shows a section through an embodiment of a contact force testingapparatus with measuring sensor;

FIG. 3 shows a view of an embodiment of a female contact element whosecontact force can be measured using the contact force testing apparatusfrom FIG. 2;

FIG. 4 shows a section through a section of the contact force testingapparatus from FIG. 2 with details of the measuring sensor;

FIG. 5 shows an enlarged section through a section of the contact forcetesting apparatus from FIG. 4 with details of the contact region of themeasuring sensor;

FIG. 6 shows an enlarged section through a section of the contact forcetesting apparatus from FIG. 5 with details of the structure of themeasuring sensor;

FIG. 7 shows a perspective view of the contact force testing apparatusfrom FIG. 2;

FIG. 8 shows a cross-section through a section of the contact forcetesting apparatus from FIG. 5 with details of the structure of themeasuring sensor in the contact region;

FIG. 9 shows a section through a section of the contact force testingapparatus from FIG. 4 with details of the protective cap and on theprotective sleeve of the measuring sensor;

FIG. 10 shows a section through a section of the measuring sensor fromFIG. 9 with details of the protective sleeve of the measuring sensor inthe contact region; and

FIG. 11 shows a section through a section of the measuring sensor fromFIG. 9 with details of the protective sleeve of the measuring sensor inthe fastening region.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

FIG. 1 shows in schematic view an electrical plug connection. Theelectrical plug connection comprises a male contact element in the formof a contact pin 1 and it has a female contact element in the form of acontact socket 2. The contact pin 1 can be reversibly contacted with thecontact socket 2. To this end, the contact pin 1 is inserted into thecontact socket 2 so that the two contact elements overlap in certainareas. The contact pin 1 is shown by a dot-and-dash line in thecorresponding region of the contact overlap. A tight fit takes place ina contact region 3 characterized by delimiting dashed lines. The contactsocket 2 is slotted in the region of the contact overlap, for example, aplurality of contact socket lamellae 21, 21′ are spaced apart from oneanother in certain areas by at least one contact socket slot 22 and thusform a spring element. A contact force F is produced by outward bendingof this spring element. The contact socket 2 can comprise a pluralityof, for example, six contact socket lamellae. The contact elements aremade of metallic material such as copper, copper alloys etc. Thediameter of the contact pin 1 lies in the range of 0.35 mm to 25.4 mm.Depending on the size of the contact elements, the contact force F is inthe range of 1 N to 10 N. Knowing the present invention, the springelement can also be mounted on the male contact element, as in a 4 mmcotter pin (banana plug).

FIG. 2 shows a section through an embodiment of a contact force testingapparatus 10 with measuring sensor 100. The measuring sensor 100 can becontacted with a female contact element in the form of a contact socket2 depicted in FIG. 3. Measuring sensor 100 and contact socket 2 have alargely circularly symmetrical structure in relation to a central axisXX′. An elongate extension of measuring sensor 100 and contact socket 2runs parallel to the central axis XX′ thereof. In FIGS. 2, 4, 7 and 9,the central axis XX′ of the measuring sensor 100 is drawn at a centralpoint of the measuring sensor 100. FIGS. 2, 4, 5, 6 and 9 are cut awayin the direction of a thickness extension of the measuring sensor 100.The thickness extension of the measuring sensor 100 runs normal to theelongate extension of the measuring sensor 100. Details of the measuringsensor 100 are depicted in FIG. 4. Details of a contact region 3 of themeasuring sensor 100 are shown in FIGS. 5 to 8. Details of a protectivesleeve 107 of the measuring sensor 100 are shown in FIGS. 9 to 11.Knowing the present invention, a person skilled in the art can modifythe measuring sensor in order to contact the measuring sensor with amale contact element

In order to measure a contact force F of the female contact element, themeasuring sensor 100 is positioned relative to the central axis XX′obliquely below the spring element of the female contact element.Oblique designates angles which differ from 0° or 180°. Angles of 0° or180° are designated as parallel. The contact force F is measured as anormal contact force which acts normally to the central axis XX′ andtherefore parallel to the thickness extension of the measuring sensor100. In FIG. 6 the contact force F is shown by a force arrow. Themeasuring sensor 100 has a protective cap 111 in a front region. Themeasuring sensor 100 comprises piezoelectric material 102, 103 in thecontact region 3. The measuring sensor 100 is inserted into the femalecontact element via the protective cap 111. In this case, the protectivecap 111 slides over an inner surface of the female contact element untilthe contact region 3 of the measuring sensor 100 is positionedunderneath the spring element of the female contact element. In order tokeep the wear in this position as low as possible, the protective cap111 is made of abrasion-resistant material such as stainless steel,steel alloys etc. and has a tapering tip as insertion aid. Naturally theprotective cap 111 itself cannot be too abrasion-resistant in order notto damage the female contact element by abrasion during measurement ofthe contact force.

The measuring sensor 100 receives the contact force F in the contactregion 3 via the piezoelectric material 102, 103. As shown in FIG. 6,the measuring sensor 100 also has an acceptor electrode 104 which iscompletely surrounded by piezoelectric material 102, 103 in the contactregion 3 in the direction of the thickness extension of the measuringsensor 100 and receives the polarization charges. The beginning and endof the contact region are characterized by dashed lines, for example, inFIGS. 4 to 6. Protective cap 111 and contact region 3 are arranged alongthe elongate extension of the measuring sensor 100. Finally, as shown inFIGS. 5-7, the measuring sensor 100 is attached to a carrier 110 in afastening region. The contact force testing apparatus 10 can be fastenedin a stable fixed position by means of the carrier 110. The carrier 110is made of mechanically resistant material such as stainless steel,steel alloys etc.

The piezoelectric material 102, 103 can consist of piezoelectric crystalsuch as (SiO₂ single crystal), calcium-gallo-germanate (Ca₃Ga₂Ge₄O₁₄ orCGG), langasite (La₃Ga₅SiO₁₄ or LGS), tourmaline, galliumorthophosphate, etc. However, the piezoelectric material 102, 103 canalso consist of piezo-ceramics such as barium titanate (BaTiO₃),mixtures (PZT) of lead titanate (PbTiO₃) and lead zirconate (PbZrO₃),etc. as well as piezoelectric polymers such as polyvinylidene fluoride(PVDF), polyvinylfluoride (PVF), polyvinylchloride (PVC), etc. Themeasuring sensor 100 comprises at least two layers of piezoelectricmaterial 102, 103 having a thickness of less than/equal to 200 μm. Whenusing piezoelectric material 102, 103 comprising piezoelectric crystal,the layers are cut as plate-shaped or rod-shaped elements having adefined crystal orientation. If the piezoelectric material 102, 103consists of piezoelectric crystal, the contact force testing apparatus10 can be used at operating temperatures at least equal to 100° C.,preferably at operating temperatures in the range of 140° C. to 160° C.,preferably at operating temperatures less than or equal to 600° C. Ifthe piezoelectric material 102, 103 consists of piezoelectric polymers,the layers are available as thin films. The piezoelectric material canbe deposited in commonly used thin-film methods with defined crystalorientation.

The layers of piezoelectric material 102, 103 are metallized on one orboth sides. The metallization can be accomplished by thermolaminationwith a metal film or by deposition of metal. Copper, copper alloys,gold, gold alloys, aluminium, aluminium alloys, silver, silver alloys,etc. can be used as metal.

The layers of piezoelectric material 102, 103 are orientedcrystallographically so that under the action of the contact force F,the electric polarization charges on one layer side are produced aselectrically negative surface charges and on the other layer side aselectrically positive surface charges. In order to receive theelectrically negative surface charges, the layers of piezoelectricmaterial 102, 103 on the side of the generated electrically negativesurface charges are provided with a first metallization. In order toreceive the electrically positive surface charges, the layers ofpiezoelectric material 102, 103 on the side of the generatedelectrically positive surface charges are provided with a second andthird metallization.

However, the first metallization is also used as joining material. Thisis because, in order to increase the sensitivity of the measuring sensor100 and in order to be able to further process the piezoelectricmaterial 102, 103 using commonly used manufacturing methods, as shown inFIG. 6, two layers of piezoelectric material 102, 103 are connected toone another in a firmly bonded manner by means of their firstmetallizations. This firmly bonded connection is made by diffusionwelding (thermocompression bonding), soldering, adhesive bonding usingelectrically conductive adhesive material etc. Thus, the firmly bondedinterconnected first metallizations form an acceptor electrode 104 inthe form of a layer of metallic material. The acceptor electrode 104 isdisposed between two adjacent layers of piezoelectric material 102, 103and receives its electrically negative surface charges. This acceptorelectrode 104 is a factor of 2, preferably a factor of 10, thinner thanacceptor electrodes from the prior art. Advantageously the thickness ofthe first metallizations is greater than/equal to the maximum roughnessof the piezoelectric material 102, 103. This ensures that the metal ofthe first metallizations can diffuse well during diffusion welding atrelatively low metallization temperatures between 100° C. and 450° C.and that after the diffusion welding this metal thus largely covers allthe surface regions of the interconnected layers of piezoelectricmaterial 102, 103. This is because at such relatively low temperaturesthe piezoelectric material 102, 103 does not diffuse or only diffusesslightly. Consequently, the acceptor electrode 104 can largely receiveall electrically negative surface charges which in turn results inhigh-quality output signals with low hysteresis of less than/equal to 3%FSO and high linearity of less than/equal to 3% FSO, where FSO is theabbreviation for Full Scale Output, or in German, Vollbereichssignal.The layer of metallic material thus formed has a thickness of lessthan/equal to 5 μm.

As shown in FIG. 5, the polarization charges received by the acceptorelectrode 104 are removed via an electrical conductor 109, 109′ and canbe evaluated. For a simple and secure electrical connection of theelectrical conductor 109, 109′ with the acceptor electrode 104, a firstlayer of piezoelectric material 102 in the direction of the elongateextension of the measuring sensor 100 is configured to be longer than asecond layer of piezoelectric material 103. According to FIGS. 4 and 5,the first layer of piezoelectric material 102 in the direction of thethickness extension of the measuring sensor 100 is arranged closer tothe central axis XX′ and is configured to be longer in certain areas.The first layer of piezoelectric material 102 has a first metallizationon the side facing away from the central axis XX′. In the area where thefirst layer of piezoelectric material 102 is configured to be longer,the first metallization of the first layer of piezoelectric material 102is exposed and is accessible for an electrical connection to theelectrical conductor 109, 109′. This electrical connection can be firmlybonded and can be accomplished by diffusion welding, adhesive bondingusing electrically conductive adhesive material etc. However, thiselectrical connection can also be non-positive and be accomplished byspring contact, etc. In each case, a layer of piezoelectric material 102is thus electrically connected to an electrical conductor 109, 109′. Theelectrical conductor 109, 109′ is in turn electrically connected to acharge amplifier not shown, which charge amplifier converts the receivedpolarization charges into a voltage directly proportional thereto.

As shown in FIGS. 5, 6 and 7, the measuring sensor 100 comprises a baseplate 101 which is disposed in the direction of the elongate extensionof the measuring sensor 100. The base plate 101 is made of mechanicallyresistant material such as stainless steel, steel alloys, ceramics,Al₂O₃ ceramics etc. As shown in FIGS. 4 to 6, the first layer ofpiezoelectric material 102 is connected on one side in a firmly bondedmanner to the base plate 101 and the second layer of piezoelectricmaterial 103 is connected on one side in a firmly bonded manner to acover plate 105. The cover plate 105 is made from the stiffest possiblematerial such as stainless steel, steel alloys, ceramics, Al₂O₃ ceramicsetc. For the firmly bonded connection to the layers of piezoelectricmaterial 102, 103, base plate 101 and cover plate 105 can be metallized.The stiffness is obtained from the elastic modulus of the material ofthe cover plate 105 and the geometry of the cover plate 105. A highstiffness gives a small change in volume and a high eigenfrequency undermechanical stresses which results in high-quality output signals withlow hysteresis of less than/equal to 3% FSO and high linearity of lessthan/equal to 3% FSO.

In order to receive the electrically positive surface charges, the firstlayer of piezoelectric material 102 is provided with a secondmetallization on the side of the generated electrically positive surfacecharges. As shown in FIG. 6, a firmly bonded connection 106 of the firstlayer of piezoelectric material 102 with the base plate 101 isaccomplished by diffusion welding of the second metallization with thebase plate 101. And in order to receive electrically positive surfacecharges, the second layer of piezoelectric material 103 is provided witha third metallization on the side of the generated electrically positivesurface charges. A firmly bonded connection 108 of the second layer ofpiezoelectric material 103 with the cover plate 105 is made by diffusionwelding of the third metallization to the cover plate 105. Knowing thepresent invention, the person skilled in the art can also implement thefirmly bonded connections 106, 108 by soldering or by adhesive bondingusing electrically conductive adhesive material etc. The second andthird metallizations serve as a counterelectrode for receiving theelectrically positive surface charges of the two layers of piezoelectricmaterial 102, 103. The counterelectrode is electrically connected to thecharge amplifier by means of electrical conductors not shown. As shownin FIG. 8, the outer side of the cover plate 105 facing away from thecentral axis XX′ is convexly shaped. This outer side has a radius ofcurvature which largely corresponds to the distance of the base plate101 from the central point of the measuring sensor 100 to the coverplate 105.

As shown in FIG. 3, the female contact element 2 in the embodiment of acontact socket as spring element has six contact socket lamellae 21, 21′which are spaced apart in certain areas by contact socket slots 22. Thecontact force F of this female contact element 2 can be measured usingthe contact force testing apparatus 10 from FIG. 2. For this purpose themeasuring sensor 100 as shown in FIGS. 7 and 8 has six piezoelectricpick-ups 11, 11′. Each piezoelectric pick-up 11, 11′ is connectedmechanically to the base plate 101. Preferably the piezoelectricpick-ups 11, 11′ are connected via the second metallization of the firstlayer of piezoelectric material 102 to the base plate 101 in a firmlybonded manner. Each piezoelectric pick-up 11, 11′ comprises a firstlayer of piezoelectric material 102 with second metallization, anacceptor electrode 104 and a cover plate 105 with third metallization.The first layer of piezoelectric material 102 is connected to the baseplate 101 in the contact region 3 via a side facing the central axisXX′. The acceptor electrode 104 is connected to the first layer ofpiezoelectric material 102 in the contact region 3 via a side facing thecentral axis XX′. The second layer of piezoelectric material 103 isconnected to the acceptor electrode 104 in the contact region 3 via aside facing the central axis XX′. The cover plate 105 is connected tothe second layer of piezoelectric material 103 in the contact region viaa side facing the central axis XX′. Width and length of a piezoelectricpick-up 11, 11′ in the contact region 3 correspond to those of a contactsocket lamella 21, 21′. In relation to the central axis XX′ of thefemale contact element 2 and the measuring sensor 100, the contactsocket lamellae 21, 21′ and the piezoelectric pick-ups 11, 11′ arearranged rotationally offset with respect to one another. For example,the piezoelectric pick-ups 11, 11′ are arranged symmetricallyrotationally offset with respect to one another with an angle of therotational offset which is obtained from the angular magnitude of thefull circle of 360° divided by the number of piezoelectric pick-ups 11,11′, in the present case therefore with an angle of rotational offset of60°. Adjacent piezoelectric pick-ups 11, 11′ are spaced apart from oneanother by a pick-up gap 12, 12′. In relation to the central axis XX′,during insertion of the measuring sensor 100 into the female contactelement 2, precisely one of the piezoelectric pick-ups 11, 11′ comes tolie in the contact region non-positively under precisely one contactsocket lamella 21, 21′. Knowing the present invention, the personskilled in the art can arrange more or fewer piezoelectric pick-ups 11,11′ with a rotational offset to one another. In the case of fourpiezoelectric pick-ups 11, 11′, the angle of the rotational offset is90°, in the case of eight piezoelectric pick-ups 11, 11′, the angle ofthe rotational offset is 45°. The spring force of the contact socketlamellae 21, 21′ can thus be measured individually or integrally. In thecase of individual measurement of the spring force, each piezoelectricpick-up 11, 11′ measures the contact force F of a contact socket lamella21, 21′. In the case of integral measurement of the spring force, allthe piezoelectric pick-ups 11, 11′ measure the contact force F of allthe contact socket lamellae 21, 21′. In this way, it can be determinedwhether the contact force F of individual contact socket lamellae 21,21′ meets predefined desired values or whether the contact force of thespring element of the female contact element 2 meets predefined desiredvalues.

As shown in FIGS. 5-11, the measuring sensor 100 comprises amembrane-like protective sleeve 107. During contact of the measuringsensor 100 with the electrical contact element 1, 2, the protectivesleeve 107 abuts directly against the electrical contact element 1, 2.The protective sleeve 107 fulfils at least one of the followingfunctions: it protects the piezoelectric pick-ups 11, 11′, it protectsthe pick-up gaps 12, 12′ and it protects the electrical conductors 109,109′ of the measuring sensor 100. The protective sleeve 107 protectsagainst harmful environmental influences such as impurities (dust,moisture etc.). Such impurities disadvantageously influence the lifetimeand the availability of the measuring sensor 100. To this end theprotective sleeve 107 through its mechanical extension prevents thepenetration of such impurities into the measuring sensor 100. However,the protective sleeve 107 also protects against electrical andelectromagnetic interference effects in the form of electromagneticradiation and thus enables the electromagnetic compatibility of themeasuring sensor 100 and therefore of the contact force testingapparatus 10. To this end, the protective sleeve 107 is made ofelectrically conductive material and absorbs interfering electromagneticradiation and diverts resulting electric currents. As a result of itsmechanical extension, the protective sleeve 107 is an electric shieldingof the measuring sensor 100. Protective sleeve 107, protective cap 109and carrier 110 form an electrical shielding of the measuring sensor100.

Details of the protective sleeve 107 are shown in FIGS. 5 to 11. Theprotective sleeve 107 for example rests flush against the protective cap111 in a front region of the measuring sensor 100 and in a rear regionof the measuring sensor 100 is connected in a firmly bonded manner tothe carrier 110. This firmly bonded connection is made by welding, laserwelding, soldering, adhesive bonding using electrically conductiveadhesive material etc. The electrical conductors 109, 109′ form anelectrical connection with the first metallization of the first layer ofpiezoelectric material 102. This electrical connection is completelycovered from the outside by the protective sleeve 107 relative to thecentral axis XX′. The protective sleeve 107 is made of material such asstainless steel, steel alloys, etc. The protective sleeve 107 iscircularly symmetrical in the contact region 3 and in the contact region3 completely covers from the outside the piezoelectric pick-ups 11, 11′and the pick-up gaps 12, 12′ relative to the central axis XX′. A radiusof curvature of the outer side of the cover plate 105 is less than orequal to an inner radius of the protective sleeve 107. As shown in FIG.10, the protective sleeve 107 is very thin in the contact region 3, witha thickness of less than or equal to 200 μm, preferably 50 μm. Formounting, the piezoelectric pick-ups 11, 11′ are mechanically connectedto the base plate 101 and the protective sleeve 107 is pulled in thedirection of the elongate extension of the measuring sensor 100 over thepiezoelectric pick-ups 11, 11′ connected mechanically to the base plate101. The protective sleeve 107 thus lies non-positively on the outersides of the cover plates 105 and biases the layers of piezoelectricmaterial 102, 103 with a defined bias with respect to the base plate101. Knowing the present invention, protective sleeve 107 and protectivecap 111 can also be produced in one piece.

REFERENCE LIST

XX′ Central axis

F Contact force

1 Contact pin

2 Contact socket

3 Contact region

10 Contact force testing apparatus

11, 11′ Piezoelectric pick-ups

12, 12′ Pick-up gaps

21, 21′ Contact socket lamella

22 Contact socket slot

100 Measuring sensor

101 Base plate

102 First layer of piezoelectric material

103 Second layer of piezoelectric material

104 First metallization or pick-up electrode

105 Cover plate

106 Second metallization

107 Protective sleeve

108 Third metallization

109, 109′ Electrical conductors

110 Carrier

111 Protective cap

The invention claimed is:
 1. A testing apparatus for measuring a contactforce applied by a female electrical contact element of a femaleelectrical connector, which is configured for effecting electricalconnection with a male electrical contact element, the apparatuscomprising: a measuring sensor having a contact region configured forbeing disposed in contact with the female electrical contact element ofthe female electrical connector when the measuring sensor is insertedinto the female electrical connector in place of the male electricalcontact element, the measuring sensor including a plurality ofpiezoelectric pick-ups disposed in the contact region, each of theplurality of piezoelectric pick-ups including piezoelectric material;each of the plurality of piezoelectric pick-ups being disposed-spacedapart from one another by a respective one of a plurality of pick-upgaps; and a protective sleeve made of electrically conducting materialthat covers the plurality of piezoelectric pick-ups and the plurality ofpick-up gaps in the contact region and wherein the protective sleeve isconfigured to be disposable between the female electrical contactelement and the plurality of piezoelectric pick-ups when the measuringsensor is inserted into the female electrical connector.
 2. The contactforce testing apparatus according to claim 1, wherein piezoelectricpick-ups are arranged rotationally offset with respect to one anotherabout a central axis of the measuring sensor; and that the protectivesleeve completely covers from the outside the piezoelectric pick-ups andthe pick-up gaps with respect to the central axis in the contact region.3. The contact force testing apparatus according to claim 1, wherein theprotective sleeve abuts non-positively against the piezoelectricpick-ups in the contact region.
 4. The contact force testing apparatusaccording to claim 1, wherein the measuring sensor has a base platewhich is disposed in the direction of an elongate extension of themeasuring sensor; and that the piezoelectric pick-ups are connectedmechanically to the base plate.
 5. The contact force testing apparatusaccording to claim 4, wherein each piezoelectric pick-up has a firstlayer of piezoelectric material which is connected in the contact regionvia a side facing the central axis to the base plate; that eachpiezoelectric pick-up has an acceptor electrode which is connected inthe contact region via a side facing the central axis to the first layerof piezoelectric material; that each piezoelectric pick-up has a secondlayer of piezoelectric material which is connected in the contact regionvia a side facing the central axis to the acceptor electrode; that eachpiezoelectric pick-up has a cover plate which is connected in thecontact region via a side facing the central axis to the second layer ofpiezoelectric material.
 6. The contact force testing apparatus accordingto claim 5, wherein the first layer of piezoelectric material has afirst metallization on a side facing away from the central axis; that anelectrical conductor is connected electrically to the firstmetallization; and that the protective sleeve completely covers thiselectrical connection from the outside with respect to the central axis.7. The contact force testing apparatus according to claim 5, wherein anouter side of the cover plate facing away from the central axis isconvexly shaped in the contact region; that the protective sleeve iscircularly symmetrical in the contact region; and that a radius ofcurvature of the outer side of the cover plate is less than or equal toan inner radius of the protective sleeve.
 8. The contact force testingapparatus according to claim 1, wherein the protective sleeve has athickness of less than or equal to 50 μm, in the contact region.
 9. Thecontact force testing apparatus according to claim 1, wherein themeasuring sensor has a protective cap in a front region; that themeasuring sensor has a support in a rear region; that the protectivesleeve abuts flush against the protective cap in the front region of themeasuring sensor; and that the protective sleeve is connected in afirmly bonded manner to the support in the rear region of the measuringsensor.
 10. The contact force testing apparatus according to claim 1,wherein due to its mechanical extension, the protective sleeve preventsthe penetration of impurities into the measuring sensor.
 11. The contactforce testing apparatus according to claim 1, wherein due to itsmechanical extension, the protective sleeve forms an electricalshielding of the measuring sensor.
 12. The contact force testingapparatus according to claim 1, wherein the protective sleeve abutsdirectly against the electrical contact element upon contact of themeasuring sensor with the electrical contact element.
 13. An apparatusaccording to claim 1, wherein each of the piezoelectric pickups isarranged symmetrically rotationally offset by a rotational offset anglefrom each other one the piezoelectric pickups, which rotational offsetangle is obtained from the angular magnitude of the full circle of 360°divided by the number of piezoelectric pickups.
 14. An apparatusaccording to claim 13, wherein each of the plurality of pick-up gaps inthe contact region is devoid of solid material.
 15. An apparatusaccording to claim 1, wherein the contact region is defined within acylindrical region formed about a central axis, and wherein each of theplurality of piezoelectric pick-ups is disposed within the cylindricalregion.
 16. An apparatus according to claim 1, wherein a first one ofthe plurality of piezoelectric pick-ups defines a clockwise sidedisposed facing toward a clockwise direction around the circumferentialdirection within the cylindrical region, wherein a second one of theplurality of piezoelectric pick-ups is disposed nearest to the clockwiseside and spaced apart from the first one of the plurality ofpiezoelectric pick-ups by one of the plurality of pick-up gaps, which isdevoid of solid material.